H33.ai has anchored a new cryptographic construction, H33-74, to the Bitcoin mainnet, establishing a 74-byte footprint for post-quantum security after initially processing three independent signature families totaling 21,063 bytes. This move follows research indicating quantum computers may pose a threat to Bitcoin with fewer resources than previously estimated, prompting a response from the Florida-based firm. H33-74 simultaneously commits to ML-DSA-65, FALCON+, and SLH-DSA-SHA2-128f, each built on distinct mathematical problems to bolster security through diversification. “Post-quantum keys will get heavier, and H33-Substrate will stay 74 bytes forever,” said Eric Beans, CEO of H33.ai, emphasizing the construction’s enduring efficiency as quantum computing power increases.
H33-74: Canonical Commitment Substrate & 74-Byte Footprint
A new cryptographic primitive, H33-74, achieves quantum-level security with a small permanent data footprint of 74 bytes, a contrast to the increasing size of most post-quantum cryptographic solutions. H33.ai, Inc. recently filed a patent application for H33-74, also known as the Canonical Commitment Substrate, and simultaneously verified its construction on the Bitcoin mainnet just two weeks after research highlighted increased quantum computing threats to Bitcoin’s security. The core innovation is H33-74’s ability to distill these three algorithms, which originally totaled 21,063 bytes, into a fixed-width 74-byte commitment. This is achieved through a 58-byte substrate commitment and a 42-byte receipt, with a 32-byte hash anchoring on-chain and the receipt stored off-chain. The company demonstrated the system’s compatibility with Bitcoin by anchoring the first H33-74 attestation in a standard transaction using Bitcoin Core 28.0, requiring no software updates or soft forks.
H33-74 supports unbounded Merkle aggregation, allowing a single transaction to commit to a vast number of attestations, potentially exceeding one quadrillion, with minimal per-result attestation costs. At a sustained throughput of 2,175,029 attestations per second, the hardware cost per computation is approximately 3.8 × 10⁻¹⁰. This computation-agnostic primitive can attest to diverse data types, from Bitcoin transactions to AI inferences, and is available commercially with a launch rate of 0.025 per mint.
ML-DSA-65, FALCON+, SLH-DSA: Tri-Algorithm Security Foundations
The pursuit of quantum-resistant cryptography has largely focused on increasing key sizes and computational demands, but H33.ai has taken a different path, introducing a cryptographic primitive, H33-74, that permanently compresses three independent post-quantum signature algorithms into 74 bytes. This contrasts with individual signature sizes like SLH-DSA, which can reach 17,088 bytes, or a combined total of 21,063 bytes for a three-family bundle. This multi-algorithm approach aims to maximize resilience through diversity; forging an H33-74 attestation necessitates breaking all three underlying cryptographic assumptions. The construction’s formal security is deliberately set to NIST Level 1, prioritizing this assumption diversity. This was achieved without modifying Bitcoin’s consensus rules or requiring a soft fork, leveraging the capacity for embedding fixed-width data in transaction outputs introduced with the Taproot activation in November 2021.
Post-quantum keys will get heavier, and H33-Substrate will stay 74 bytes forever. Post-quantum cryptography was supposed to make everything heavy and slow. H33 makes it lighter and faster than today.”
Eric Beans, CEO, H33.ai
Bitcoin Mainnet Verification & Taproot Anchoring Method
The company filed a United States patent application covering H33-74, a cryptographic primitive designed to compress three independent post-quantum signature families, ML-DSA-65, FALCON+, and SLH-DSA-SHA2-128f, into a fixed 74-byte footprint. This represents a departure from the trend of increasing data size associated with post-quantum cryptography, as the system permanently maintains this compact size regardless of the complexity of the underlying signatures. On April 14, 2026, H33.ai anchored the first attestation to the Bitcoin mainnet using a standard transaction with both a Taproot P2TR output and an OP_RETURN output, demonstrating compatibility with existing infrastructure without requiring a soft fork. This anchoring method leverages Bitcoin’s existing Taproot capability, activated in November 2021, to embed fixed-width data within transaction outputs. The system’s scalability is noteworthy; a single transaction can commit to a batch of N attestations, limited only by available memory, with per-leaf inclusion proofs scaling logarithmically.
Unbounded Merkle Aggregation & 0.025 Per-Mint Pricing
The ability to verify vast amounts of data with minimal on-chain footprint is now possible thanks to H33-74, a new cryptographic primitive from H33.ai, which allows for unbounded Merkle aggregation within a fixed cost structure. Unlike previous post-quantum schemes that increased signature sizes, H33-74 commits to three independent post-quantum signature algorithms, ML-DSA-65, FALCON+, and SLH-DSA-SHA2-128f, using a consistent 74-byte footprint, regardless of the amount of data attested. This efficiency stems from a design that prioritizes diversity in cryptographic assumptions; forging an attestation requires breaking all three underlying mathematical problems, rather than relying on the security of a single algorithm. The architecture leverages Bitcoin’s existing Taproot functionality, embedding fixed-width data in transaction outputs to create a universal post-quantum attestation anchor. The economic model is also innovative; billing is metered directly through the Bitcoin blockchain, ensuring transparency and eliminating disputes. “The launch rate is 0.025 per mint,” stated H33.ai, with a free tier of 10,000 mints available for developers.
